The Anthracite region is the site of several decollements, many large fold systems, and numerous thrust, reverse, and bedding faults. A few of these structural features extend southwestward into Maryland and West Virginia.

Detailed surface and mining data in the Anthracite region and less-detailed data in the areas on the southwest suggest that the Folded Appalachians of Pennsylvania are characterized by decollements that formed at widespread well-defined changes in rock competency. Originating at and rising from each decollement are numerous folds and faults.

Competent rocks between two decollements commonly are flexed into large simple fold systems and are displaced by a relatively few large faults. In contrast, incompetent rocks between decollements are flexed characteristically into extremely complex fold systems cut by numerous small faults. The decollements functioned as stress adjustment zones separating differentially deforming blankets of relatively competent rocks from relatively incompetent rocks.

Many of the larger anticlines appear to have formed in overlying rocks where a decollement ramped upward through a part of the sedimentary rocks section.

The Folded Appalachians of Pennsylvania probably are separated at depth from the Precambrian basement by a master decollement.

Northwestward gravity sliding induced by vertical uplift of the core of the Appalachians and supplemented by lateral compression as the core moved upward seems the most logical explanation for the tectonics of the Folded Appalachians of Pennsylvania.

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